1. Field of the Invention
The present invention relates to a device and method for detecting a disconnection of an assembled battery system constructed by connecting a plurality of secondary battery cells in series and, more particularly, to monitoring and detecting the disconnection between each cell.
2. Detailed Description of Related Art
In association with a device for monitoring a charge/discharge state of an assembled battery, such as is described in JP2004-1040989A, a disconnection between the assembled battery and the monitoring device is detected. Serial circuits each having a resistor element R and FET_Q are connected in parallel to the respective cells S. Upon detecting the disconnection, in a set of two, upper and lower cells, the upper FET turns off and the lower FET turns on. Then, when the common line between the two cells, such as the upper negative side cell and the lower positive side cell, is disconnected, the abnormality detection circuit at the upper side detects an over-charge and the abnormality detection circuit at the lower side detects an over-discharge. When the detection state is acquired, the disconnection can be detected.
However, disadvantages arise according to the device described in JP2004-104989A. For example, in a case where a total voltage of the two cells is less than an over-charge detection threshold value due to the low cell voltage, the disconnection can not be detected. In a case where the assembled battery and the monitoring device are designed such that the cell voltage varies in a range of 2 V to 4V at a normal time, the over-charge is detected when the cell voltage is 4.5V and the over-discharge is detected when the cell voltage is 1.5V, since a sum of the voltage is made 4V if the voltage of each cell is 2V, the over-charge resulting from, for example, a disconnection, can not be detected.
Even when the cell voltage is high, the disconnection of the power lines at the uppermost side, such as at the positive side of cell Sn, and at the lowermost side, such as at the negative side of cell S1, can not be detected. It should be noted that in such a situation, while the over-discharge can be detected, the disconnection can not be discerned. Thus, as described, whether the detection of the disconnection is possible disadvantageously depends on the condition.